Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ico!vail!scottw
From: scottw@ico.ISC.COM (Scott Wiesner)
Newsgroups: comp.sys.ibm.pc
Subject: Re: VGA cards: 8-bit vs. 16-bit
Message-ID: <15904@vail.ICO.ISC.COM>
Date: 6 Jul 89 15:16:56 GMT
References: <7964@cbnews.ATT.COM>
Organization: Interactive Systems Corp, Boulder, CO
Lines: 38

From article <7964@cbnews.ATT.COM>, by cbema!las@cbnews.ATT.COM (cbema!las):
> In article <8529@attctc.DALLAS.TX.US> chasm@attctc.DALLAS.TX.US (Charles Marslett) writes:
>>In article <[267.1]comp.sys.ibm.pc;1@vpnet.UUCP>, kji@vpnet.UUCP (Ken Isacson) writes:
>>>[16-bit vga cards are about twice as fast as 8 bit cards]
> 
>>[Not necessarily.  Only for 256-color modes (ignoring quality of device
>>driver software).]
> 
> Since Charles is from STB systems, this lends credibility to his remarks.
> I would still like to know, however, has anyone made an effort to measure
> and compare the differences?  Will whoever does so publish this informat-
> ion if it is not already published?  If published, where?  

I don't have measurements that I can give out, but I can say that for 
the X server I've worked on, the difference between 8 bit and 16 bit
cards is very minimal in the standard 16 color VGA modes.  As Charles
mentioned, you get a bit of an advantage with 16 bit cards since the i/o
is really 16 bit, but other than that, the EGA/VGA is still basically
an 8 bit device.  The problem is that everything you do one one of these
cards goes through a set of 8 bit wide latches.  Driving 16 bits of data
at once to the card just makes the card do 2 8 bit operations.  In fact, 
due to the programming model for the VGA, you often are forced to do
8 bit operations anyway.  

Now that I've said all that, I'll also say that the way things have
worked out, there does tend to be a bit of a difference between 8 and
16 bit cards.  The 16 bit cards tend to be newer, slightly better
designs, resulting in better operation.  The Headland (formerly Video 7)
cards are definately faster that other cards.  The Tseng Labs based 
cards (STB, Orchid, Genoa, etc) aren't as fast, but seem to be a 
very good value.  

If you're really concerned about performance, wait 6 months and go for
one of the 8514/A clones that will be coming out.  For around $1000, 
you'll get 1024x768 with 256 colors, and some hardware assist in the
area that needs it the most (bitblit).  

Scott